Pore Environment Engineering in Al-MOFs Enables Thermodynamic–Kinetic Synergy for High-Resolution Chromatographic Separation

Aluminum-based metal–organic frameworks (Al-MOFs) are recognized as promising materials for chromatographic separation, but achieving an optimal thermodynamic–kinetic balance for the separation of aromatic isomers remains challenging. Herein, we demonstrated a ligand functionalization strategy to tune the pore environment and separation performance of frl -topology Al-MOFs. By the introduction of methoxy (OMe) and cyclopentyloxy (OCp) groups into the parent Al-L-H framework, three isostructural materials (Al-L-H, Al-L-OMe, and Al-L-OCp) were obtained. The introduction of alkoxy side chains reduced porosity and modulated host–guest interactions. Mechanistic analyses revealed that OMe substitution simultaneously weakened adsorption strength and enhanced molecular diffusion, achieving an optimal thermodynamic–kinetic balance. Thus, Al-L-OMe exhibited the highest separation efficiency among the three MOFs, with a resolution of 13.74 for p -xylene and o -xylene, surpassing most reported MOF-based stationary phases. This study provides a fundamental understanding of how pore environment engineering through ligand design can harmonize thermodynamic and kinetic effects, offering an effective route toward high-performance stationary phases.